1. Field of the Invention
The present invention relates to a photoresist stripper composition for use in removing photoresist from a substrate such as a silicon wafer, and to a method for stripping photoresist using the photoresist stripper composition.
2. Description of the Related Art
In the manufacture of semiconductor devices such as integrated circuits (ICs), large scale integrated circuits (LSIs), and liquid crystal displays (LCDs), photoresists are extensively used as a coating mask material. In a common method for fabricating ICs by photolithography with a photoresist, the photoresist is evenly deposited on a conductive metal layer or a dielectric layer formed on a substrate, so that a photoresist layer is formed thereon. Then, the solvent contained in the photoresist layer is vaporized by a soft baking process so as to stabilize the photoresist layer. After the soft baking process, the photoresist layer is exposed to UV radiation, electron-beams, X-rays and so forth, and then subjected to a developing process to form a photoresist pattern on the substrate. Following this, the underlying conductive metal layer or the dielectric layer is selectively etched using the photoresist pattern as a mask, thereby forming fine circuit patterns. Thereafter, the photoresist is removed using a stripper.
In the photolithography process, it is also important to remove photoresist present on the edge or backside of the wafer after the soft baking process. Otherwise, defects can occur during a subsequent etching or ion implantation process, thereby lowering yield. A stripper containing an organic solvent is commonly used for this purpose.
Likewise, wafers undergoing reworking, which have been previously identified as defective or which have been set aside for testing, must also have photoresist removed by application of a stripper.
When the photoresist pattern from the developing process is subjected to post exposure baking (PEB) at a high temperature, ion implantation and DUV radiation, the photoresist pattern is hardened, and made more resistant to an organic solvent by cross-linking.
In removing the cured photoresist material, a solvent containing halogenated hydrocarbons and phenolic hydrocarbons has been used in the prior art. However, use of such solvents is disfavored because it causes hazardous working conditions and environmental concerns over the handling of waste matter.
Also, acidic or alkali strippers can be used to remove the cured photoresist material. However, the acidic or alkali strippers can corrode an underlying metal on the substrate, which may be an aluminum (Al) layer, or a metal alloy layer containing copper (Cu) or tungsten (W). This may limit the capacity for forming microminiature interconnection patterns.
When a common organic solvent is used as a photoresist stripper, an organic solvent such as isopropyl alcohol must be used as a rinsing solution. Thus, the rinsing process becomes complicated and the safety concerns arise.
Some conventional chemicals or solvents for use as a photoresist stripper have a very slow dissolution rate over the cured photoresist, or cause incomplete dissolution over the same. Such photoresist residues from the stripping process are not removed completely during subsequent processes, thereby adversely effecting the reliability of a device in terms of its electrical properties.
Therefore, there is a need for a photoresist stripper which is capable of completely and quickly removing the cured photoresist from the substrate without causing damage or contamination to the substrate.
Also, as the integration density of semiconductor devices increases, the fabrication of semiconductor devices becomes complicated by the need for fine line pattern formation. 1-Gigabit or more semiconductor devices, in which a pattern size has a design rule of 0.2 xcexcm or less, cannot be achieved by a conventional resist which is sensitive to light from a KrF eximer laser (248 nm). For this reason, a novel photolithography technique using an ArF eximer laser (193 nm) as an exposure light source has been introduced.
Therefore, there is a need for a photoresist stripper composition capable of being used, regardless of the polarity of photoresist, for a variety of photoresists including conventional photoresists, such as i-line resist and G-line resist, which contain Cresol Novolak Resin as a major component, and chemically amplified resists sensitive to an eximer laser or a DUV exposure light source, with the photoresist stripper composition also having a high solubility with respect these photoresists.
It is a first objective of the present invention to provide a photoresist stripper composition which is capable of effectively and quickly stripping photoresist coated on a substrate regardless of the kind and the polarity of the photoresist.
It is a second objective of the present invention to provide a photoresist stripper composition which is capable of efficiently and safely stripping photoresist coated on a substrate, either cured or uncured, without causing damage or contamination to an underlying layer.
It is a third objective of the present invention to provide a photoresist stripper composition which is capable of effectively and efficiently stripping photoresist from a wafer during a rinsing step on the edge or backside of the wafer, or during a reworking process on wafers which have defects or which were previously used for testing.
It is a fourth objective of the present invention to provide a method for stripping photoresist, by which photoresist can be effectively removed from a substrate without the need of performing an additional rinsing process with an organic solvent after stripping.
To achieve the above objectives of the present invention, there is provided a photoresist stripper composition comprising a mixture of acetone, xcex3-butyrolactone, and an ester solvent.
Preferably, the ester solvent comprises acetic acid ester. Preferably, the ester solvent comprises at least one selected from the group consisting of n-butyl acetate, amyl acetate, ethyl acetoacetate, isopropyl acetate and propylene glycol monomethyl ether acetate.
Preferably, the mixture of the photoresist stripper composition comprises: 3 to 35% by weight acetone; 2 to 13% by weight xcex3-butyrolactone; and 55 to 95% by weight ester solvent, based on the total weight of the mixture.
More preferably, the mixture of photoresist stripper composition comprises: 8 to 15% by weight acetone; 4 to 7% by weight xcex3-butyrolactone; and 80 to 90% by weight ester solvent, based on the total weight of the mixture.
Preferably, the photoresist stripper composition further comprises a surfactant.
According to another aspect of the present invention, there is provided a photoresist stripping method comprising spraying a photoresist stripper composition comprising a mixture of acetone, xcex3-butyrolactone and an ester solvent, over a substrate while rotating the substrate at a relatively low speed, so as to strip photoresist from the substrate. The rotation of the substrate is stopped for a short period of time, and thereafter the photoresist stripper composition is sprayed over the substrate while rotating the substrate at a relatively high speed. Then, the substrate is rinsed with pure water.
Preferably, after stopping the rotation of the substrate for a short period of time, the photoresist stripping method further comprises spin drying the substrate.
Preferably, after spraying the photoresist stripper composition over the substrate while rotating the substrate at a relatively high speed, the photoresist stripping method further comprises spin drying the substrate.
The photoresist stripper composition according to the present invention is effective in removing a variety of photoresists at room temperature. Also, the photoresist stripper composition has a rapid dissolution rate and is very volatile, and thus it does not remain on the surface of the wafer after stripping. In addition, the method for stripping photoresist with the photoresist stripper composition can completely remove photoresist from the wafer surface, and is itself removed by simple rinsing step with water, thereby simplifying the overall process.